Superconducting quantum critical point in CeCoIn(5-x)Sn(x).

We report a combined pressure-doping study in the nearly two-dimensional heavy fermion superconductor CeCoIn5 as its superconducting phase is driven to the normal state by Sn doping and/or applied pressure. Temperature-pressure-dependent electrical resistivity measurements were performed at the vicinity of a superconducting quantum critical point where Tc→0. A universal plot of the concentration- and pressure-dependent phase diagram suggests that for the concentrations studied a single mechanism is responsible for reducing Tc and bringing the system to the superconducting quantum critical point. A two-band model with hybridization controlled by pressure and doping provides a consistent description of the phase diagram and the suppression of the d-wave superconductivity in this material.

Spin rotation induced by applied pressure in the Cd-doped Ce2RhIn8 intermetallic compound.

The pressure evolution of the magnetic properties of the Ce2RhIn7.79Cd0.21 heavy fermion compound was investigated by single crystal neutron magnetic diffraction and electrical resistivity experiments under applied pressure. From the neutron magnetic diffraction data, up to P = 0.6 GPa, we found no changes in the magnetic structure or in the ordering temperature T N = 4.8 K. However, the increase of pressure induces an interesting spin rotation of the ordered antiferromagnetic moment of Ce2RhIn7.79Cd0.21 into the ab tetragonal plane. From the electrical resistivity measurements under pressure, we have mapped the evolution of T N and the maximum of the temperature dependent electrical resistivity (T MAX) as a function of the pressure (P ≲ 3.6 GPa). To gain some insight into the microscopic origin of the observed spin rotation as a function of pressure, we have also analyzed some macroscopic magnetic susceptibility data at ambient pressure for pure and Cd-doped Ce2RhIn8 using a mean-field model including tetragonal crystalline electric field (CEF). The analysis indicates that these compounds have a Kramers doublet Γ 7 - -type ground state, followed by a Γ 7 + first excited state at Δ1 ∼ 80 K and a Γ6 second excited state at Δ2 ∼ 270 K for Ce2RhIn8 and Δ2 ∼ 250 K for Ce2RhIn7.79Cd0.21. The evolution of the magnetic properties of Ce2RhIn8 as a function of Cd doping and the rotation of the direction of the ordered moment for the Ce2RhIn7.79Cd0.21 compound under pressure suggest important changes of the single ion anisotropy of Ce3+ induced by applying pressure and Cd doping in these systems. These changes are reflected in modifications in the CEF scheme that will ultimately affect the actual ground state of these compounds.

Large variations in the magnetic ordering behavior of EuCu(2)As(2) with the application of external pressure and magnetic field.

The influence of external pressure on the electrical transport and magnetic properties of EuCu(2)As(2), crystallizing in a ThCr(2)Si(2)-type structure, is reported. The system is known to be an antiferromagnet below T(N) ≈ 15 K in the absence of external magnetic fields. We find that there is a gradual reduction of T(N) with the application of a magnetic field with an extrapolated value of the critical field of around 18 kOe which can drive T(N) to zero. Electrical resistivity under pressure (<11 GPa) reveals that the magnetic ordering temperature is pushed up dramatically to higher temperatures which is quite interesting if compared with the behavior in isostructural FeAs-based systems containing Eu. Above 7 GPa, the pressure-induced state appears to be ferromagnetic. The results thus reveal interesting changes in the magnetic ordering behavior of this compound with increasing pressure and magnetic fields.

Tuning the pressure-induced superconducting phase in doped CeRhIn5.

Pressure- and temperature-dependent heat capacity and electrical resistivity experiments on Sn- and La-doped CeRhIn5 are reported for two samples with specific concentrations, Ce(0.90)La(0.10)RhIn5 and CeRhIn(4.84)Sn(0.16), which present the same TN=2.8 K. The obtained P-T phase diagrams for doped CeRhIn5 compared to that for the pure compound show that Sn doping shifts the diagram to lower pressures while La doping does exactly the opposite, indicating that the important energy scale to define the pressure range for superconductivity in CeRhIn5 is the strength of the on-site Kondo coupling.